CLI Reference

Commands

zwasm run / zwasm <file>

Execute a WebAssembly module. The run subcommand is optional — zwasm file.wasm is equivalent to zwasm run file.wasm.

zwasm <file.wasm|.wat> [options] [args...]
zwasm run <file.wasm|.wat> [options] [args...]

By default, calls _start (WASI entry point). Use --invoke to call a specific exported function.

Examples:

# Run a WASI module (calls _start)
zwasm hello.wasm --allow-all

# Run a WAT text format file (no compilation needed)
zwasm program.wat

# Call a specific exported function
zwasm math.wasm --invoke add 2 3

Argument types

Function arguments are type-aware: zwasm uses the function’s type signature to parse integers, floats, and negative numbers correctly.

# Integers
zwasm math.wat --invoke add 2 3          # → 5

# Negative numbers (no -- needed)
zwasm math.wat --invoke negate -5        # → -5
zwasm math.wat --invoke abs -42          # → 42

# Floating-point
zwasm math.wat --invoke double 3.14      # → 6.28
zwasm math.wat --invoke half -6.28       # → -3.14

# 64-bit integers
zwasm math.wat --invoke fib 50           # → 12586269025

Results are displayed in their natural format:

• i32/i64: signed decimal (e.g. -1, not 4294967295)
• f32/f64: decimal (e.g. 3.14, not raw bits)

Argument count is validated against the function signature:

zwasm math.wat --invoke add 2             # error: 'add' expects 2 arguments, got 1

WASI modules

WASI modules use _start and receive string arguments via args_get. Use -- to separate WASI args from zwasm options:

# String args passed to the WASI module
zwasm app.wasm --allow-all -- hello world
zwasm app.wasm --allow-read --dir ./data -- input.txt

# Environment variables (injected vars accessible without --allow-env)
zwasm app.wasm --env HOME=/tmp --env USER=alice

# Sandbox mode: deny all + fuel 1B + memory 256MB
zwasm untrusted.wasm --sandbox
zwasm untrusted.wasm --sandbox --allow-read --dir ./data

Multi-module linking

# Link an import module and call a function
zwasm app.wasm --link math=math.wasm --invoke compute 42

Resource limits

# Limit instructions (fuel metering) and memory
zwasm untrusted.wasm --fuel 1000000 --max-memory 16777216

zwasm inspect

Show a module’s imports and exports.

zwasm inspect [--json] <file.wasm|.wat>

# Human-readable
zwasm inspect examples/wat/01_hello_add.wat

# JSON output (for scripting)
zwasm inspect --json math.wasm

Options:

• --json — Output in JSON format

zwasm validate

Check if a module is valid without executing it.

zwasm validate <file.wasm|.wat>

zwasm features

List supported WebAssembly proposals.

zwasm features [--json]

zwasm version

Print the version string.

zwasm help

Show usage information.

Run options

Execution

WASI capabilities

Resource limits

Debugging

Batch mode

With --batch, zwasm reads invocation commands from stdin, one per line:

add 2 3
mul 4 5
fib 10

echo -e "add 2 3\nmul 4 5" | zwasm math.wasm --batch --invoke add

Exit codes